Display devices incorporating liquid crystal light valve structures are well known in the art. A liquid crystal light valve is a multilayer structure. Among the various layers in the multilayer structure is a transparent conductor or electrode film on which has been deposited a photosensor layer.
The transparent conductor or electrode film must provide adequate conductivity in a plane and adequate light transmission through the plane. An alloy of In.sub.2 O.sub.3 :Sn is commonly used for this purpose and is referred to in the art as an ITO film. Such films may be deposited on a suitable fiber optics substrate, such as glass, by chemical reaction, evaporation or by sputtering, a technique also well known in the art.
A commonly used material for the photosensor layer or film is cadmium sulfide (CdS). Photosensor layers of CdS can be formed by precipitation from solution, evaporation and by sputtering. U.S. Pat. Nos. 3,976,361 and 4,025,339 contain much background information on the films herein mentioned and deposition techniques.
Display devices employing conventional liquid crystal light valves to be used on the Space Shuttle Mission Simulator showed objectionable image retention when the display changed from highlight to lower brightness displays. The image retention problem manifested itself as a negative of the previous image superimposed on the current image in the display. The problem was ultimately determined to reside in the CdS photosensor layer or film in the liquid crystal light valve.
It is an object of this invention to provide an improved photosensor layer or film of CdS, the film and a liquid crystal light valve employing said film exhibiting minimum image retention time while maintaining acceptable sensitivity. It is also an object of this invention to provide an improved process for producing the aforementioned photosensor layer or film of CdS. Other objects will become apparent from the description of the invention.